I like the page preview option (command + mouse hover on a link), but it doesn’t provide much utility b/c you can’t do anything with the preview (e.g., scroll, select text, etc.). Perhaps this is part of the pending pane improvements (and maybe even remotely related to some of the transclusion discussions, e.g., Fully transclude backlinks), but the ability to scroll, select text, etc. on the page preview would be very useful.
Moreover, it would be powerful if the page preview has the option to become a floating pane or a pane that can be snapped.